Phosphorus and sulfur containing



Ferdinand P. Otto, Woodbury,

PHOSPHORUS AND SULFUR CONTAINING ANTIOXIDANT N. 3., assignor to SoconyMobil Oil Company, Inc, a corporation of New York No Drawing.Application January 17, 1952, Serial No. 267,009

15 Claims. or. 252-325 This invention relates to reaction productscapable of improving the oxidationand corrosion-resisting properties ofmineral lubricating oils. It is more particularly concerned withreaction products of phosphorus sulfide with alkyl disulfides andthiocyanates, and the metal salts thereof.

As is well known to those familiar to the art, it has been proposed toreact many materials with phosphorus sulfides, to produce productscapable of improving the properties of lubricants. Thus, there have beenreacted with phosphorus pentasulfide olefins of several types, petroleumfractions, terpenes, alcohols, mercaptans, etc. In so far as is nowknown, however, it has never been known that effective antioxidants canbe produced by reacting alkyl disulfides or thiocyanates with phosphoruspentasulfide.

It has now been discovered that certain reaction products of this typeimpart improved properties to lubricants. It has now been discoveredthat the reaction products of relatively high molecular weightdisulfides or thiocyanates with phosphorus pentasulfide, and metal saltsof the disulfide reaction product effectively improve the resistance ofmineral lubricating oils to oxidation and to corrosion. Accordingly, itis a broad object of the present invention toprovide lubricants havingimproved resistance to oxidation and to corrosion. A further object isto provide novel addition agents for mineral lubricating oils. Anotherobject is to provide lubricating oils containing novel phosphorus andsulfur-containing additives. A specific object isto provide reactionproducts of alkyl thiocyanates or disulfides with phosphoruspentasulfide, and salts thereof, and mineral lubricating oils containingthem. Other objects and advantages of the present invention will becomeapparent to those skilled in-the art, from the following detaileddescription.

Broadly stated, the present invention provides a mineral lubricating oilcontaining a small amount, suificient to improve the resistance thereofto oxidation, of an antioxidant of the group consisting of (1) areaction product of an alkyl thiocyanate, having at least about 12carbon atoms per alkyl radical, with phosphorus pentasulfide, (2) thereaction product of an alkyl disulfide, having at least about 12 carbonatoms per alkyl radical, with phosphorus pentasulfide, and (3) analkaline-earth metal salt of said alkyl disulfide-phosphoruspentasulfide reaction product.

The alkyl thiocyanates and alkyl disulfides which are reacted withphosphorus pentasulfide to produce the reaction products of thisinvention have the respective formulae, RSCN and RSS-R, wherein R is analkyl radical. The alkyl radicalsfin the foregoing formulae shouldcontain at least 12 carbon atoms and up to about 34 carbon atoms. Theseradicals can be straight-chain or branched-chain alkyl radicals.Especially preferred are the alkyl thiocyanates and disulfides havingbetween about 21 and about 34 carbon atoms per alkyl radical,particularly the wax thiocyanates and disulfides. Nonlimiting examplesof the thiocyanate and disulfide reactants are dodecyl thiocyanate,isododecyl disulfide, tetradecyl thiocyanate, heptadecyl disulfide,octadecyl disulfide, eicosyl thiocyanate, heneicosyl thiocyanate,docosyl disulfide, Z-methyltricosyl thiocyanate, isohexacosyl disulfide,tetracontyl thiocyanate, paraffin wax disulfide, paraffin waxthiocyanate, ozokerite disulfide, ceresin wax thiocyanate, slack waxdisulfide, and scale wax thiocyanate.

The alkyl thiocyanates and disulfides contemplated herein are well knownto those familiar to the art. Several methods for their preparation areavailable. For example, a feasible method is described in a copending:Otto application, Serial Number 267,008, filed January 17, 1952. Some ofthese materials are also available commercially. Any alkyl thiocyanateor alkyl disulfide is 1 utilizable for the purposes of the presentinvention, re

gardless of its source.

pentasulfide is utilizable herein.

In order to ensure complete reaction between the phosphorus pentasulfidereactant and the alkyl thiocyanate or alkyl disulfide, a weight excessof phosphorus pentasulfide should be used. Due to its insolubility inthe final re-- action product, unreacted phosphorus pentasulfide is:

readily removed, as by filtration. In general, the amount; of phosphoruspentasulfide used will be between about: 0.25 mole and about one molethereof per mole of thio cyanate or disulfide reactant.

The reaction between the phosphorus pentasulfide and the alkylthiocyanate or disulfide is effected at a temperature of between aboutC. and about 200 C. The lower temperatures, around about 100 (3., yielda product having a relatively high acidity. On the other hand,temperatures of between about C. and about 200 C. favor the formation ofreaction products having a relatively lower acidity. For the purposes ofthis invention, products produced at any temperature within the rangeaforedefined are effective antioxidants.

The reaction contemplated herein is usually complete in between aboutone hour and about five hours. In practice, a reaction time of betweenabout two and about three hours is sufiicient. Generally, the highermolecular weight reactants require more time for complete reaction, inaccordance with the present invention. Likewise, of course, the reactiontime will vary with the reaction temperature selected.

The use of a solvent in the present reaction is not generally necessary.If desired, a hydrocarbon solvent can be used. A solvent is oftenindicated, however, especially if the final reaction product tends to beviscous, tacky, or waxy. For practical reasons, it is desirable toprepare the reaction product in a mineral oil solvent, thus producing aconcentrate, for ease .in handling during blend ing operations. Betweenabout 25 per cent and about 75 per cent, by weight, of the entiresolution of oil and product can be mineral oil. Such a mineral oilsolvent can be a lighter oil than the mineral lubricating oil to beimproved, or it can be substantially the same, or the same. This is amatter of preference with the user.

Due to the complexity of the final reaction products, since themechanism involved in the present reaction is not known, no structuralformulae can be assigned to the reaction products. Accordingly, it willbe appreciated. that any definition of the reaction products, other thana definition reciting the method of preparing them, is highlyinaccurate.

As mentioned hereinbefore, metal salts of the alkyl disulfide-phosphoruspentasulfide reaction product are alsoetfective antioxidants andanticorrosion agents. The preferred salt-forming metals are thealkaline'earth metals,

i. e., barium, calcium, magnesium, strontium, and beryllium. It must beunderstood, however, that other saltforming metals, commonly used toprepare mineral oil additives, can be employed and are contemplatedherein.

Suchmetals include zinc, aluminum, cobalt, nickel, and

the like.

The metal salts of the alkyl disulfide-phosphorus pentasulfide reactionproducts are substantially neutral salts. In other words, the reactionproduct is completely neutralized. Salt formation is effected by any ofthe several methods knownto the art. The salts can be formed, forexample, by first preparing the alkali-metal, e. g., the sodium salt andthen effecting a double decomposition reaction With a soluble inorganicsalt of the desired metal, e. g., barium nitrate, calcium chloride, etc.The salts can also be produced by heating the reaction product with anoxide or hydroxide of the desired metal, at temperatures above theboiling point of water, in order to drive off water of neutralization.If desired, a low-boiling solvent, such as, a lower alcohol, benzene,toluene, etc., can be employed, in order to remove water by azeotropicdistillationn It must be noted, however, that the particular methodselected for salt formation is not a critical factor.

Since the metal salts of the reaction products, as contemplated herein,tend to be viscous or waxy, it is desirable to prepare them in thepresence of a mineral oil solvent. Between about 25 per cent and about75 per cent, by weight, of the final solution of salt and oil, can bemineral oil. As described hereinbefore, the mineral oil solvent can belight or heavy, dependent upon individual preference.

The following specific examples are for the purpose of demonstrating thebest methods for preparing the additives of this invention, and todemonstrate the effectiveness thereof. Although wax reaction productsare illustrated, it is to be strictly understood that this invention isnot to be limited to the specific reactants used in the examples, or tothe operations and manipulations involved therein. As those familiarwith the art will understand, a wide variety of other reactants andconditions, as defined hereinbefore, can be used.

ALKY L THIOCYANATE-PzSs PRODUCTS Example 1 A mixture of 100 grams ofparaflin wax thiocyanate and grams of phosphorus pentasulfide washeated, with agitation, at a temperature of about 100 C., for threehours. The hot reaction mixture was then filtered through filtering clayon a steam-heated funnel, in order to remove unreacted phosphoruspentasulfide. The product thus obtained, i. e., the filtrate, was abrown, waxy material containing, by weight, 14.6 per cent sulfur, 2.4per cent nitrogen, and 4.04 per cent phosphorus, and having aneutralization number of 93.

The wax thiocyanate employed herein was the product described anddefined in Example 2 of the copending application, Serial Number267,008, filed January 17, 1952.

Example 2 A mixture of 63 grams of wax thiocyanate (as defined inExample 1), 7.5 grams of phosphorus pentasulfide, and 63 grams ofmineral oil was heated, with agitation, at 170 C. for three hours. Thereaction mixture was then cooled to ambient temperature (about C.) andan additional 63 grams of mineral oil was added. The mixture was thenfiltered through filtering clay on a steam-heated funnel, to removeunreacted phosphorus pentasulfide. The filtered product was a lightbrown oil containing, by weight, 5.66 per cent sulfur, 1.62 per centnitrogen, and 1.33 per cent phosphorus, and having a neutralizationnumber of 6.6. The mineral oil used herein was a solvent-refined,Midcontinent stock having a Saybolt Universal Viscosity of 67 seconds at210 F., a specific gravity of 0.890 and a flash point of 405 F.

4 ALKYL DISULFIDE-P2S5 PRODUCT Example 3 A mixture of grams of waxdisulfide and 20 grams of phosphorus pentasulfide was heated, withagitation, at a temperature of about 150 C. for 2.5 hours. The reactionmixture was then filtered to remove unreacted phosphorus-pentasulfide.The filtrate was a light brown material, waxy at room temperatures,containing, by weight, 18.8 per cent sulfur and 5.43 per centphosphorus, and having a neutralization number of 88.5.

The wax disulfide used in this example was the product described anddefined in Example 3 of copending application, Serial Number 267,008,filed January 17, 1952.

METAL SALT OF ALKYL DISULFIDE-P2S5 PRODUCT Example 4 A mixture of 63grams of the wax disulfide-P285 product of Example 3, 63 grams ofmineral oil, 20 grams of barium hydroxide octahydrate, and cubiccentimeters of n-butanol was placed in a reaction vessel provided with amechanical stirrer, thermometer, and a condenser inverted fordistillation. The mixture was gradually heated, with. agitation, to C.,until water and alcohol had ceased to distil (about two hours). Thereaction mixture was then cooled to room temperature (about 20 C.) anddiluted with about 100 cubic centimeters of benzene. Then the dilutedmixture was filtered through filtering clay to remove unreacted bariumhydroxide. The solvents (benzeneand residual butanol) were removed bytopping at 150C. under reduced pressure. The product was a light brownoil containing, by weight, 5.12 per cent barium, 5.6 per cent sulfur,and 1.48 per cent phosphorus.

TEST DATA Example 5 The products described in Examples 1 through 4 wereblended, at various concentrations, in portions of a solvent-refinedPennsylvania mineral oil having an A. P. I. gravity of 30.2, a flashpoint of 435 F., and a viscosity of 63.12 centistokes at 100 F. and of8.45 centistokes at 210 F. This is a typical motor oil stock. Theresultant blends were subjected to the Bubble Test. In this test, 30grams of the test oil is placed in a large testtube containing a weighedpiece of cadmium-silver bearing, and provided with a gas inlet tubeextending to the bottom thereof. The test tube is maintained at C. inaconstant temperature bath. Air is blown through the oil, at the rate oftwo liters per hour, for 22 hours. At the end of the test, the piece ofbearing is removed and reweighed. Results are reported in terms ofmilligrams loss in weight of the bearing. Test results obtained hereinare set forth in Table I.

TABLE I.BUBBLE TEST- RESULTS Mg. Loss in Weight Inhibitor g InhibitedUnlnhlb- Oil lted 011 Product of'Ex. 1 0. 125 0 23 Do 0.063 0 23 Do r 0.032 2 23 Product of Ex. 2. 0. 5 0 28 D0 0. 25 0 28 D0 0. 125 O 28Product of Ex 3 0. 25 0 21 Do 0. 125 0 21 Do 0 063 0 21 Product of Ex 4.0.25 0 28 Do 0.125 0 28 Do 0.063 0 28 Example 6 A blend of two per cent,by weight, of the product of Example 4 in a motor oil stock wasprepared. This .011 is a solvent-refined Pennsylvania stock having an A.P. I. gravity of 31.7, a flash point of 395 F., and

a viscosity of 36.4 centistokes at 100 F. and 5.71 centistokes at 210 F.The blend was subjected to a 36-hour Lauson engine test. The oil wasplaced in a single cylinder, 4-cycle Lauson engine operated at an oiltemperature of 250-260 F., at a speed of 1815 R. P. M., using a 13:1air-fuel ratio. No oil was added during the test. The neutralizationnumber and the viscosity at 210 F. of .the oil are determined at the endof the test. These values, when compared with similar values for theuninhibited base oil, indicate the oxidation tendencies of the test oilunder service conditions.

When subjected to this test, the'oil blend had a neutralization numberof 1.1 and a kinematic viscosity of 6.35 centistokes at 210 F. Theuninhibited oil, when subjected to the same test, showed aneutralization number of 7.3 and a viscosity of 8.21 centistokes at 210F. Accordingly, under the specifications of this test, the test blend israted as excellent.

Example 7 In a solvent-refined Pennsylvania mineral oil base stockhaving an A. P. I. gravity of about 30.2, a flash point of 435 F., and aviscosity of 63.12 centistokes at 100 F. and 8.45 centistokes at 210 F.,was blended two per cent by weight of the product of Example 4. Thisblend was subjected to the C. F. R. corrosion test. In this test, a C.F. R. fuel test engine, from which all equipment applying only to fueltest work has been removed, is used. Oil at a controlled temperature isdelivered by a metering pump from an external heating sump to the testconnecting rod bearing, through the drilled crankshaft. All other engineparts are lubricated with oil drawn from the same external sump by adouble capacity C. F. R. oil pump. A copper-lead alloy test bearing isplaced in the large end of the connecting rod. The jacket temperatureismaintained at about 212 F., and the oil temperature at about 285 F.During the test, the compression ratio and engine speed are maintainedat 5.5 and 1200 R. P. M., respectively. The engine is operated for astandard time which has been taken as the time (in hours) required for aloss of about 0.200 gram of the copper-lead alloy test bearing when ablank oil is used. The effectiveness of an oil addition agent ismeasured by the time required for a similar loss when a blend of thesame oil and an addition agent is used. The neutralization numbers ofthe blank oil and of the oil blend were determined after several timeintervals, as were the bearing losses of the test bearings. Test resultsfor the blend and for the uninhibited base oil are set forth in TableII.

6 rust agents, defoamants, and other additives well known tothoseskilled in the art.

Although the present invention has been described in conjunction withpreferred embodiments, modifications and variations are contemplated, asthose skilled in the art will readily understand. Such variations andmodifications are considered to be Within the purview and scope of theappended claims.

a What is claimed is:

1. As a new composition of matter, an antioxidant selected from thegroup consisting of 1) the reaction product of an alkyl thiocyanate,having between about 21 and about 34 carbon atoms per alkyl radical,with phosphorus pentasulfide, (2) the reaction product of an alkyldisulfide, having between about 21 and about 34 carbon atoms per alkylradical, with phosphorus pentasulfide, and (3) an alkaline-earth metalsalt of said alkyl disulfide-phosphorus pentasulfide reaction product.

2. The reaction product of an alkyl thiocyanate, having between about 21and about 34 carbon atoms per alkyl radical, with phosphoruspentasulfide.

3. The reaction product of a parafiin wax thiocyanate with phosphoruspentasulfide.

4. The reaction product of an alkyl disulfide, having between about 21and about 34 carbon atoms per alkyl radical, with phosphoruspentasulfide.

5. The reaction product of a parafiin wax disulfide with phosphoruspentasulfide.

6. An alkaline-earth metal salt of the reaction product of a paraifinwax disulfide with phosphorus pentasulfide.

7. The barium salt of the reaction product of a petroleum wax disulfidewith phosphorus pentasulfide.

8. A mineral lubricating oil containing a small amount, sufficient toimprove the resistance thereof to oxidation, of an antioxidant selectedfrom the group consisting of (1) the reaction product of an alkylthiocyanate, having between about 21 and about 34 carbon atoms per alkylradical, with phosphorus pentasulfide, 2) the reaction product of analkyl disulfide, having between about 21 and about 34 carbon atoms peralkyl radical, with phosphorus pentasulfide, and (3) an alkaline-earthmetal salt of said alkyl disulfide-phosphorus pentasulfide reactionproduct.

9. A mineral lubricating oil containing between about 0.05 per cent andabout 10 per cent by weight of an antioxidant selected from the groupconsisting of (1) the reaction product of an alkyl thiocyanate, havingbetween about 21 and about 34 carbon atoms per alkyl radical, withphosphorus pentasulfide, (2) the reaction product of an alkyl disulfide,having between about 21 and about TABLE II.C. F. R. CORROSION TEST 20Hrs. 41 Hrs. 47 Hrs. 63 Hrs. 85 Hrs 107 Hrs.

G. G. G. G. G. a Loss Loss Loss Loss Loss Loss Unlnhtblted Oil 0. 014 174 0. 135 3. 5 0. 235 0i1+2% Product of Ex. 4 0.005 0. 9 0 009 1- 7 0.025 2. 8 0.073 3. 6 O. 181 4. 0

Neutralization number.

weight concentrations of between about 0.5 per cent and about 4 percent.

It will be appreciated that other addition agents can be added to themineral oil along with the additives of this invention, in order toimprove other properties of the oil. Thus, for example, the oil blendcan also contain oiliness agents, E. P. additives, V. I. improvers,anti- 34 carbon atoms per alkyl radical, with phosphorus pentasulfide,and 3) an alkaline-earth metal salt of said alkyl disulfide-phosphoruspentasulfide reaction product.

10. A mineral lubricating oil containing a small amount, suflicient toimprove the resistance thereof to oxidation, of the reaction product ofan alkyl thiocyanate, having between about 21 and about 34 carbon atomsper alkyl radical, with phosphorus pentasulfide.

11. A mineral lubricating oil containing a small amount, sufficient toimprove the resistance thereof to oxidation, of the reaction product ofa parafiin wax thiocyanate with phosphorus pentasulfide.

12. A mineral lubricating oil containing a small amount," suflicientto-improve the-resistance thereof to oxidation, of the reaction productof an alkyl disulfide,

13. A mineral lubricating oil containing a 'small 'amount, suffic'ientto 'improve'the resistance thereof to oxidation, of the reaction productof'a paraffin wax disulfide with phosphorus pentasulfide.

14. A mineral lubricating oil' containing asmall amount, sulficient toimprove 'the resistance thereof to oxidation, of an alkaline-earth metalsalt of the reaction product of a parafiin' wax disulfide withphosphorus pentasulfide.

15.'A miner'al'lubricating oil containing a small amount,-sufiicient toimprove the*resistan'ce"thereof-to 0Xidation,'-of the barium saltofthereaction-product of a petroleum wax-disulfide with-phosphorusp'entasulfidc.

References Cited in the file of this patent UNITED STATES PATENTS2,150,400 Rosen Mar. 14, 1939 2,169,700 Loane'et al 'Al 1g. 15, 19392,209,440 Adams etal. 'July30, 1940 2,316,091 'White Apr. 6, 19432,516,119 Hersh July 25, 1950

1. AS A NEW COMPOSITION OF MATTER, AN ANTIOXIDANT SELECTED FROM THEGROUP CONSISTING OF (1) THE REACTION PRODUCT OF AN ALKYL THIOCYANATE,HAVING BETWEEN ABOUT 21 AND ABOUT 34 CARBON ATOMS PER ALKYL RADICAL,WITH PHOSPHORUS PENTASULFIDE, (2) THE REACTION PRODUCT OF AN ALKYLDISULFIDE, HAVING BETWEEN ABOUT 21 AND ABOUT 34 CARBON ATOMS PER ALKYLRADICAL, WITH PHOSPHORUS PENTASULFIDE, AND (3) AN ALKALINE-EARTH METALSALT OF SAID ALKYL DISULFIDE-PHOSPHORUS PENTASULFIDE REACTION PRODUCT.